The present invention relates to a safety valve designed to be fitted to a hydraulic circuit of the kind used to control machines, machine tools and construction plants, in aircraft and on various kinds of vehicles. A circuit of this kind is generally controlled by at least one hydraulic distributor.
As is well known, a hydraulic circuit of the aforementioned type usually includes flexible hoses controlling the rams or the like, for example, in order to manipulate a load. A safety problem arises should a hose supplying a ram rupture.
The invention is directed to overcoming this problem and ensuring the safety of users even in the event of rupture of a hose in a circuit controlling the manipulation of a load. In the case of manipulating loads it is particularly directed to enabling immobilization of the load during lifting and, during lowering, normal continuance of this movement and/or halting thereof on command.
To this end the invention proposes a safety valve on permanent standby normally authorizing flow of fluid in only one direction between its inlet and outlet, flow of fluid in the opposite direction requiring the application of a control pressure which is normally applied by the controller but which, in the event of rupture of a hose, can result from a pressure threshold being exceeded at the outlet.
To this end the invention further proposes a safety valve for a hydraulic circuit supplying a hydraulic receiver having an inlet and an outlet connected to the receiver and characterized in that it includes, between the inlet and outlet, a non-return module having a non-return valve and a selectively operable valve having an unoperated position in which the non-return valve prevents any reverse flow of fluid from the outlet to the inlet and an operated position in which such reverse flow is made possible. A control inlet is provided for applying control pressure to the selectively operable valve and a pressure relief valve is provided between the outlet and the control inlet from a predetermined pressure threshold.
It will be realized that a valve of this kind makes it possible to control fluid flow rates at a pressure of around 400 bars, for example, with control pressures of only 25 bars or less.